This invention relates to television synchronizing generator apparatus and especially to apparatus for synchronizing the television signals from two or more sources of video information, for example, two or more television cameras.
In the programming of television programs, many of the video information sources comprise television cameras which electronically scan the scene information for conversion to an electrical signal representative of the scene. It is necessary that the electrical signal representing the scene information be identified by timing signals in order that the image information may be processed, transmitted and reassembled in the same sequence as the original scanning. This timing process is generally known as synchronizing, and comprises the precision timing of the electronic scanning of the original image. Historically, the synchronizing of television signals from one or more cameras has been accomplished by means of a device known as a master synchronizing generator. In master sync systems, timing information in the form of horizontal and vertical scan timing signals, as well as blanking and color subcarrier signals, are coupled from the master sync generator to the various cameras by means of multiple conductor or coaxial cable. Television systems of the above-described form, although satisfactory for single studio use, become cumbersome when employed in multiple studio or field and portable camera use. To provide added flexibility, individual synchronizing generators have been developed which are located at all picture sources. These individual synchronizing generators, being located at the primary source of video information, are generally identified as source sync generators and the cameras being capable of stand-alone operation. However, it is still necessary, when utilizing individual source synchronizing generators, to provide a means of insuring that the timing of all of the video sources be phase coincident for efficient programming of the final television picture. To insure this phase coincidence, it is common to provide a single master reference signal in the form of an external composite signal reference to which all the video sources, such as television cameras, are locked by a process well known as Genlock. However, the use of Genlock does not insure continuous phase coincidence with the incoming reference video signal, especially in the case of source sync generators for color television signals, wherein the relative phasing of the horizontal sync pulse and the color subcarrier (burst) of the reference signal are varying.